The invention relates to an electric motor mounting structure and more specifically to a convoluted metal cylinder which is press fit circumjacent the electric motor stator and which is in turn mounted into an outer motor housing.
An electric motor generally comprises a rotor, stator, windings, bearings and an outer housing. When the motor is activated and delivering power, a torque equal in magnitude but opposite in direction to that produced by the rotor is produced in the stator and this reaction torque must be transferred from the stator to the outer housing and thence to an external support which may be a mounting plate or, in the case of a hand-held tool, the operator. The stator must be positively retained in the outer housing in order to transfer the reaction torque to it and to the external support. In industrial electrical motors which develop substantial torque, and an equally substantial reaction torque, consideration must be given to providing a stator mounting which will withstand the reaction torque loading. The retention means must be capable of transferring a reaction torque equal to the maximum torque the motor is capable of generating to the outer housing, or the stator may break away from the internal retention means. If the stator rotates inside the housing, damage to the internal wiring will invariably occur and the operator may be subjected to a shock hazard. In practice, a substantial margin of safety between the torque which the retention means is capable of resisting and the torque which the motor is capable of producing is incorporated into the design of the stator retaining structure.
Various stator and outer housing interconnecting configurations have been utilized. Attempts to mount the stator directly to the outer housing with bolts or other fasteners proved unsuccessful since this required the drilling and tapping of threaded openings in the stator which were engageable by the fasteners. The openings created discontinuities in the magnetic circuit of the stator and had a deleterious effect on the performance of the electric motor. A loss of power accompanied by overheating resulted from this type of stator mounting.
Another prior art approach required that the stator be produced with a plurality of longitudinal outwardly projecting ribs around its circumference which mated with a like number of equally spaced longitudinal channels on the inner wall of the outer housing. This structure facilitated slip-in assembly and had the advantage of uniformly distributing the reaction torque around the housing. However, this design required that the housing undergo numerous expensive machining operations to prepare it to receive the stator. Such a structure is becoming increasingly unfeasible from an economic standpoint.